Merge branch 'report_source_of_parse_errors' of ssh://github.com/mostynb/cli into mostynb-report_source_of_parse_errors

flag.go

@@ -426,19 +426,22 @@ func hasFlag(flags []Flag, fl Flag) bool {
 	return false
 }
 
-func flagFromEnvOrFile(envVars []string, filePath string) (val string, ok bool) {
+// Return the first value from a list of environment variables and files
+// (which may or may not exist), a description of where the value was found,
+// and a boolean which is true if a value was found.
+func flagFromEnvOrFile(envVars []string, filePath string) (value string, fromWhere string, found bool) {
 	for _, envVar := range envVars {
 		envVar = strings.TrimSpace(envVar)
-		if val, ok := syscall.Getenv(envVar); ok {
-			return val, true
+		if value, found := syscall.Getenv(envVar); found {
+			return value, fmt.Sprintf("environment variable %q", envVar), true
 		}
 	}
 	for _, fileVar := range strings.Split(filePath, ",") {
 		if fileVar != "" {
 			if data, err := ioutil.ReadFile(fileVar); err == nil {
-				return string(data), true
+				return string(data), fmt.Sprintf("file %q", filePath), true
 			}
 		}
 	}
-	return "", false
+	return "", "", false
 }